In the past, a control system of an internal combustion engine which is provided with an air-fuel ratio sensor in an exhaust passage of the internal combustion engine, and controls an amount of fuel fed to the internal combustion engine based on the output of the air-fuel ratio sensor, has been widely known (for example, see PLTs 1 to 4).
For example, in the control system described in PLT 1, as the air-fuel ratio sensor, a sensor which is provided with: a first electrode which is exposed to exhaust gas flowing through the inside of the exhaust passage; a second electrode which is exposed to the atmospheric air; and a solid electrolyte layer of zirconia, etc., which is arranged between the first electrode and second electrode, has been used. When using this air-fuel ratio sensor to detect the air-fuel ratio of the exhaust gas (below, also referred to as “exhaust air-fuel ratio”), a 0.4V voltage is applied across these electrodes and the current flowing across these electrodes is detected as the output current. Further, based on this output current, the exhaust air-fuel ratio is calculated.